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SubjectRe: [PATCH 04/20] virtio: Implement get_shm_region for PCI transport
On Wed, Mar 11, 2020 at 05:34:05PM +0000, Stefan Hajnoczi wrote:
> On Tue, Mar 10, 2020 at 02:19:36PM -0400, Vivek Goyal wrote:
> > On Tue, Mar 10, 2020 at 11:04:37AM +0000, Stefan Hajnoczi wrote:
> > > On Wed, Mar 04, 2020 at 11:58:29AM -0500, Vivek Goyal wrote:
> > > > diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c
> > > > index 7abcc50838b8..52f179411015 100644
> > > > --- a/drivers/virtio/virtio_pci_modern.c
> > > > +++ b/drivers/virtio/virtio_pci_modern.c
> > > > @@ -443,6 +443,111 @@ static void del_vq(struct virtio_pci_vq_info *info)
> > > > vring_del_virtqueue(vq);
> > > > }
> > > >
> > > > +static int virtio_pci_find_shm_cap(struct pci_dev *dev,
> > > > + u8 required_id,
> > > > + u8 *bar, u64 *offset, u64 *len)
> > > > +{
> > > > + int pos;
> > > > +
> > > > + for (pos = pci_find_capability(dev, PCI_CAP_ID_VNDR);
> > >
> > > Please fix the mixed tabs vs space indentation in this patch.
> >
> > Will do. There are plenty of these in this patch.
> >
> > >
> > > > +static bool vp_get_shm_region(struct virtio_device *vdev,
> > > > + struct virtio_shm_region *region, u8 id)
> > > > +{
> > > > + struct virtio_pci_device *vp_dev = to_vp_device(vdev);
> > > > + struct pci_dev *pci_dev = vp_dev->pci_dev;
> > > > + u8 bar;
> > > > + u64 offset, len;
> > > > + phys_addr_t phys_addr;
> > > > + size_t bar_len;
> > > > + int ret;
> > > > +
> > > > + if (!virtio_pci_find_shm_cap(pci_dev, id, &bar, &offset, &len)) {
> > > > + return false;
> > > > + }
> > > > +
> > > > + ret = pci_request_region(pci_dev, bar, "virtio-pci-shm");
> > > > + if (ret < 0) {
> > > > + dev_err(&pci_dev->dev, "%s: failed to request BAR\n",
> > > > + __func__);
> > > > + return false;
> > > > + }
> > > > +
> > > > + phys_addr = pci_resource_start(pci_dev, bar);
> > > > + bar_len = pci_resource_len(pci_dev, bar);
> > > > +
> > > > + if (offset + len > bar_len) {
> > > > + dev_err(&pci_dev->dev,
> > > > + "%s: bar shorter than cap offset+len\n",
> > > > + __func__);
> > > > + return false;
> > > > + }
> > > > +
> > > > + region->len = len;
> > > > + region->addr = (u64) phys_addr + offset;
> > > > +
> > > > + return true;
> > > > +}
> > >
> > > Missing pci_release_region()?
> >
> > Good catch. We don't have a mechanism to call pci_relese_region() and
> > virtio-mmio device's ->get_shm_region() implementation does not even
> > seem to reserve the resources.
> >
> > So how about we leave this resource reservation to the caller.
> > ->get_shm_region() just returns the addr/len pair of requested resource.
> >
> > Something like this patch.
> >
> > ---
> > drivers/virtio/virtio_pci_modern.c | 8 --------
> > fs/fuse/virtio_fs.c | 13 ++++++++++---
> > 2 files changed, 10 insertions(+), 11 deletions(-)
> >
> > Index: redhat-linux/fs/fuse/virtio_fs.c
> > ===================================================================
> > --- redhat-linux.orig/fs/fuse/virtio_fs.c 2020-03-10 09:13:34.624565666 -0400
> > +++ redhat-linux/fs/fuse/virtio_fs.c 2020-03-10 14:11:10.970284651 -0400
> > @@ -763,11 +763,18 @@ static int virtio_fs_setup_dax(struct vi
> > if (!have_cache) {
> > dev_notice(&vdev->dev, "%s: No cache capability\n", __func__);
> > return 0;
> > - } else {
> > - dev_notice(&vdev->dev, "Cache len: 0x%llx @ 0x%llx\n",
> > - cache_reg.len, cache_reg.addr);
> > }
> >
> > + if (!devm_request_mem_region(&vdev->dev, cache_reg.addr, cache_reg.len,
> > + dev_name(&vdev->dev))) {
> > + dev_warn(&vdev->dev, "could not reserve region addr=0x%llx"
> > + " len=0x%llx\n", cache_reg.addr, cache_reg.len);
> > + return -EBUSY;
> > + }
> > +
> > + dev_notice(&vdev->dev, "Cache len: 0x%llx @ 0x%llx\n", cache_reg.len,
> > + cache_reg.addr);
> > +
> > pgmap = devm_kzalloc(&vdev->dev, sizeof(*pgmap), GFP_KERNEL);
> > if (!pgmap)
> > return -ENOMEM;
> > Index: redhat-linux/drivers/virtio/virtio_pci_modern.c
> > ===================================================================
> > --- redhat-linux.orig/drivers/virtio/virtio_pci_modern.c 2020-03-10 08:51:36.886565666 -0400
> > +++ redhat-linux/drivers/virtio/virtio_pci_modern.c 2020-03-10 13:43:15.168753543 -0400
> > @@ -511,19 +511,11 @@ static bool vp_get_shm_region(struct vir
> > u64 offset, len;
> > phys_addr_t phys_addr;
> > size_t bar_len;
> > - int ret;
> >
> > if (!virtio_pci_find_shm_cap(pci_dev, id, &bar, &offset, &len)) {
> > return false;
> > }
> >
> > - ret = pci_request_region(pci_dev, bar, "virtio-pci-shm");
> > - if (ret < 0) {
> > - dev_err(&pci_dev->dev, "%s: failed to request BAR\n",
> > - __func__);
> > - return false;
> > - }
> > -
> > phys_addr = pci_resource_start(pci_dev, bar);
> > bar_len = pci_resource_len(pci_dev, bar);
>
> Do pci_resource_start()/pci_resource_len() work on a BAR where
> pci_request_region() hasn't been called yet? (I haven't checked the
> code, sorry...)

It should. Infact, pci_request_region() itself is calling
pci_resource_start() and pci_resource_len().

>
> Assuming yes, then my next question is whether devm_request_mem_region()
> works in both the VIRTIO PCI and MMIO cases?

It should work on MMIO case as well. This basically works on /proc/iomem
resource tree to reserve resources. So as long as MMIO memory range
has been registered by driver in /proc/iomem, it will work.

>
> If yes, then this looks like a solution, though the need for
> devm_request_mem_region() should be explained in the vp_get_shm_region()
> doc comments so that callers remember to make that call. Or maybe it
> can be included in vp_get_shm_region().

How about adding a line in include/linux/virtio_config.h right below the
@get_shm_region descrition which says.

"This does not reserve the resources and caller is expected to call
devm_request_mem_region() or similar to reserve resources."

Vivek

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